AggR, a transcriptional activator of aggregative adherence fimbria I expression in enteroaggregative Escherichia coli

Abstract

Enteroaggregative Escherichia coli (EAggEC) has been associated with persistent pediatric diarrhea in the developing world, yet the pathogenetic mechanisms of EAggEC infection are unknown. Our previous data have suggested that aggregative adherence of some EAggEC strains to HEp-2 cells is mediated by flexible, bundle-forming fimbriae, which we have termed aggregative adherence fimbriae I (AAF/I). Genes sufficient to confer expression of AAF/I are located on the 60-MDa plasmid of EAggEC 17-2; AAF/I genes are present as two unlinked plasmid regions (regions 1 and 2), separated by 9 kb of DNA. Here we report the complete DNA sequencing of region 2 and the identification of an open reading frame which is involved in the expression of AAF/I. One open reading frame of 794 bp encodes a protein (designated AggR) with a predicted molecular size of 29.4 kDa, which shows a high degree of amino acid sequence identity to CfaR and other members of the AraC class of gene regulators. The cloned aggR gene (or, alternatively, a cloned cfaR gene) was sufficient to complement a region 1 clone to confer AAF/I expression. To further substantiate the role of aggR in the regulation of AAF/I, we constructed a 289-bp in-frame aggR deletion and replaced the native gene in 17-2 by allelic exchange, using the temperature-sensitive vector pIB307. The resulting aggR deletions were negative for AAF/I expression, but expression was restored when the aggR gene (cloned into pBluescript II SK) was reintroduced into the aggR mutant. RNA slot blot experiments using a probe for the putative AAF/I pilin subunit (aggA) revealed that aggR operates as a transcriptional activator of aggA expression. aggA::phoA fusions were constructed in 17-2 and in 17-2 delta aggR. AggR was found to promote expression of the aggA gene under a variety of conditions of temperature, osmolarity, oxygen tension, and medium. At acid pH, aggA expression was maximal and was regulated by both AggR-dependent and AggR-independent mechanisms.

Mecanismos de virulencia de Escherichia coli enteropatógena

“…ECEA presenta plásmidos pAA, que codifican varios factores de virulencia, en los que se incluye un regulador AggR perteneciente a la familia de activadores transcripcionales AraC/XylS, el que se encuentra en la mayoría de las cepas; se sugirió el término "ECEA típica" a aquellas que lo expresan 87,88 .…”

Enteroaggregative Escherichia coli in diarrheic children in Egypt: molecular characterization and antimicrobial susceptibility

“…These included: pCVD432 encoding for EAEC; eaeA and bfpA for EPEC; stx1and stx2 for Shiga-like toxin 1 (SLT-1) and Shiga-like toxin 2 (SLT-2), respectively, for STEC; estA1 and estA2-4 for heat-stable (ST) and eltB for heat-labile (LT) toxins of ETEC; and ipaH for EIEC. Also, PCR techniques [14][15][16][17][18][19][20][21] were used to screen all E. coli isolates for EAEC-associated virulence genes including: aggR, a transcriptional activator; aggA, fimbriae AAFI; aafA, fimbriae AAF II; agg3A, fimbriae AAF III; astA, aggregative stable toxin 1 (EAST 1); pet, plasmid-encoded heat-labile toxin; aap, anti-aggregation protein; and pic, protein involved in colonization. In addition, ETEC-positive E. coli isolates were examined for coli surface antigens (CS) by PCR [13].…”

Expression of aggregative adherence to hela cells by Escherichia coli strains isolated from sick horses

“…The EAEC putative virulence genes described so far are located on a high molecular weight plasmid and comprise the agg and aaf operons (involved in the biogenesis of aggregative adherence fimbriae) (2,28), aggR (encoding the transcriptional activator AggR) (29), aap (formerly aspU, encoding dispersin) (34), shf (encoding a cryptic secreted protein, Shf) (9), and pet (encoding the Plasmid encoded toxin, Pet) (11). Chromosomal virulence genes have also been described in some EAEC strains, which comprise pic, encoding a Protein involved in colonization (Pic), and irp2, encoding the iron-repressible high-molecularweight protein 2 (Irp2) involved in Yersiniabactin expression (9).…”